绘制 Allegro 基元时出现奇怪的视觉错误

Question

我正在使用 allegro_primitives.h 头文件，当我用 al_draw_filled_rectangle 绘制一个矩形，并用键移动矩形时，矩形的轮廓在矩形前进的方向上正在改变颜色。代码如下：

#include <allegro5\allegro5.h>
#include <allegro5\allegro_primitives.h>
#include <iostream>
#include "Globals.h"
using namespace std;

bool keys[5] = {false, false, false, false, false};
enum KEYS {UP, DOWN, LEFT, RIGHT, SPACE};
const int WINDOW_WIDTH = 600;
const int WINDOW_HEIGHT = 600;
int main()
{
    bool done = false;
    bool redraw = true;

    ALLEGRO_DISPLAY *display = NULL;
    ALLEGRO_TIMER *timer = NULL;
    ALLEGRO_EVENT_QUEUE *event_queue = NULL;

    if(!al_init())
        return -1;

    al_set_new_display_option(ALLEGRO_SAMPLE_BUFFERS, 1, ALLEGRO_SUGGEST);
    al_set_new_display_option(ALLEGRO_SAMPLES, 8, ALLEGRO_SUGGEST);

    display = al_create_display(WINDOW_WIDTH,WINDOW_HEIGHT);

    if(!display)
        return -1;

    al_init_primitives_addon();
    al_install_keyboard();

    event_queue = al_create_event_queue();
    timer = al_create_timer(1.0 / 60);

    if(!timer)
        return -1;
    if(!event_queue)
        return -1;

    al_register_event_source(event_queue,al_get_keyboard_event_source());
    al_register_event_source(event_queue,al_get_timer_event_source(timer));
    al_register_event_source(event_queue,al_get_display_event_source(display));

    Character player;
    Character lover;

    player.x1 = 100;
    player.x2 = player.x1 + 40;
    player.y1 = (WINDOW_HEIGHT / 2) - 20;
    player.y2 = player.y1 + 40;

    lover.x1 = WINDOW_WIDTH - 140;
    lover.x2 = lover.x1 + 40;
    lover.y1 = (WINDOW_HEIGHT / 2) - 20;
    lover.y2 = lover.y1 + 40;

    al_start_timer(timer);

    while(!done)
    {
        ALLEGRO_EVENT ev;
        al_wait_for_event(event_queue,&ev);
        if(ev.timer.source == timer)
        {
            if(keys[UP])
            {
                player.y1 -= 5;
                player.y2 -= 5;
            }
            if(keys[DOWN])
            {
                player.y1 += 5;
                player.y2 += 5;
            }
            if(keys[LEFT])
            {
                player.x1 -= 5;
                player.x2 -= 5;
            }
            if(keys[RIGHT])
            {
                player.x1 += 5;
                player.x2 += 5;
            }
            if(player.x1 <= 0)
            {
                player.x1 = 0;
                player.x2 = 40;
            }
            if(player.x2 >= WINDOW_WIDTH)
            {
                player.x1 = WINDOW_WIDTH - 40;
                player.x2 = WINDOW_WIDTH;
            }
            if(player.y1 <= 0)
            {
                player.y1 = 0;
                player.y2 = player.y1 + 40;
            }
            if(player.y2 >= WINDOW_HEIGHT)
            {
                player.y1 = WINDOW_HEIGHT - 40;
                player.y2 = WINDOW_HEIGHT;
            }
        }
        if(ev.type == ALLEGRO_EVENT_DISPLAY_CLOSE)
        {
            done = true;
        }
        if(ev.type == ALLEGRO_EVENT_KEY_DOWN)
        {
            switch(ev.keyboard.keycode)
            {
            case ALLEGRO_KEY_ESCAPE:
                done = true;
                break;
            case ALLEGRO_KEY_LEFT:
                keys[LEFT] = true;
                break;
            case ALLEGRO_KEY_RIGHT:
                keys[RIGHT] = true;
                break;
            case ALLEGRO_KEY_DOWN:
                keys[DOWN] = true;
                break;
            case ALLEGRO_KEY_UP:
                keys[UP] = true;
                break;
            }
        }
        if(ev.type == ALLEGRO_EVENT_KEY_UP)
        {
            switch(ev.keyboard.keycode)
            {
            case ALLEGRO_KEY_ESCAPE:
                done = true;
                break;
            case ALLEGRO_KEY_LEFT:
                keys[LEFT] = false;
                break;
            case ALLEGRO_KEY_RIGHT:
                keys[RIGHT] = false;
                break;
            case ALLEGRO_KEY_UP:
                keys[UP] = false;
                break;
            case ALLEGRO_KEY_DOWN:
                keys[DOWN] = false;
                break;
            }
        }
        if(redraw && al_is_event_queue_empty(event_queue))
        {
            al_draw_filled_rectangle(player.x1,player.y1,player.x2,player.y2,al_map_rgb(0,0,127));
            al_draw_filled_rectangle(lover.x1,lover.y1,lover.x2,lover.y2,al_map_rgb(127,0,0));
            al_flip_display();
            al_clear_to_color(al_map_rgb(255,255,255));
        }
    }
    al_destroy_timer(timer);
    al_destroy_display(display);
    al_destroy_event_queue(event_queue);
    return 0;
}

有人可以帮我吗？ “Globals.h”只是一个小头文件，其中包含一个用于定义其 x1、x2、y1 和 y2 变量的 Character 结构。谢谢。

Answer 1

正如您当前的代码一样，您的重绘不受计时器控制。您的重绘变量被初始化为 true，但将其设置为 false 更有意义，并让您的计时器在适当的时候将其设置为 true。当你的定时器事件触发时，将 redraw 设置为 true。

ALLEGRO_EVENT ev;
al_wait_for_event(event_queue,&ev);
if(ev.timer.source == timer)
{
    redraw = true;
}

然后在检查重绘时，将其设置回 false。

if(redraw && al_is_event_queue_empty(event_queue))
{
    redraw = false;

    al_draw_filled_rectangle(player.x1,player.y1,player.x2,player.y2,al_map_rgb(0,0,127));
    al_draw_filled_rectangle(lover.x1,lover.y1,lover.x2,lover.y2,al_map_rgb(127,0,0));
    al_flip_display();
    al_clear_to_color(al_map_rgb(255,255,255));
}